An electrolyte-salt-dissolving solvent of an electric double layer capacitor, which has at least one polarizable electrode as one or both of a positive electrode and a negative electrode, is preferably stably used with a withstanding voltage of 3 V or higher. From this viewpoint, combination use of ethylene carbonate and propylene carbonate, which is a cyclic carbonate having a high oxidation potential (withstanding voltage), has been proposed (for example, see Patent Literature 1). The withstanding voltage obtainable by such combination, however, is limited to around 2.7 V at the highest.
Further, in order to improve the withstanding voltage, use of a non-aqueous solvent containing sulfolane or its derivative and specific carbonic acid chain ester (chain carbonate) (for example, see Patent Literature 2) is proposed, and in order to improve the safety, an electrolyte solution containing a specific electrolyte and fluorine-containing organic solvent in combination is proposed (for example, see Patent Literature 3).